Axial flow compressor



8- 1949. A. l. PONOMAREFF ET AL 2,478,423

AXIAL FLOW COMPRESSOR Filed Aug. 6. 1947 8O Practrvr SPEED 10 CFI M.

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INVENTORS Auxmvnzn 1. PoIveMnRlrF HNTHoNY F. Sci-Minimum WITNESSES: w). A)

ATTORNEY atcnteci Aug. 9, 1949 AL FLOW CDMPRESSOR Application August 6, 1947, Serial No. 766,504

Claims. (Cl. 230-115) The invention relates to compressors, more particularly of the axial-flow type, and it has for an object to avoid instability or surging at variable speeds.

The capacity range of a compressor, particularly of the axial-flow type, is limited by surge conditions, that is, by stalling, occurring within about 15.per cent of normal capacity. In a constant speed compressor, operation in the surge zone may be avoided by bleeding off a portion of the gas through a by-pass valve set to open at a fixed delivery pressure. While the speed of a compressor may be varied to vary the flow to suit the demand, the problem of avoiding stalling or surging is more dimcult for the reason that a bleeder or by-pass valve operated only in response to delivery pressure does not sufllce. As the surge pressure varies approximately as the square or the speed, where the compressor is operated at variable speeds, it is necessary to provide for a pressure varying approximately as the square of the speed and to use this pressure in conjunction with the delivery pressure to control by-passing, so that the by-pass valve may be normally closed with the delivery pressure capable of being increased to the point where it is able to overcome the efiect of increase in speed and start to open the by-pass valve. Assuming operation at a given speed with the by-pass valve closed, the immediate effect of an increase in speed is to move the control in the direction for closing movement of the bleeder valve; however, as the latter is already closed, the increase in speed is accompanied by increase in delivery pressure to restore the control to the position pressor pressure so that change in controlling from which it was moved due to the increase in speed, any further increase in delivery pressure being limited by the bleeder or by-pass valve being caused to open. If the compressor speed is reduced. the contrary operation takes place, the speed effect coming into play immediately to operate the control to open the by-pass valve, whereupon the decrease in delivery pressure operates the control until the valve is closed. Thus, as the compressor speed is raised and lowered, the delivery pressure is increased and decreased to maintain a normal relation as between compressor speed and delivery pressure at each speed,

any tendency for further increase in delivery pressure to bring about surging or stalling being avoided by opening of the bleeder or by-pass valve.

Accordingly, a more particular object of the invention is to provide a variable speed compresforce due to speed change is compensated by change therein due to delivery pressure change pursuant to speed change, whereby the delivery by-pass valve opens to limit the delivery pressure in relation to speed and is normally closed.

The foregoing and other objects are effected by the invention as will be apparent from the following description and claims taken in connection with the accompanying drawings, forming a part of this application, in which:

Fig. 1 is a diagrammatic view of an axial flow compressor having the present invention applied thereto;

Fig. 2 is a detail elevational view of the oil pump or impeller used to obtain a speed effect; and

Fig. 3 is a diagram.

The purpose of the present invention will be more clearly understood by first considering diagrammatic Fig. 3 wherein the lines a1, a2, etc., represent characteristics of different flows and speeds in relation to pressures. With increase in speed, the pressure changes at an increasing rate in relation to speed change with the result that operation becomes more critical as the speed is increased. it becoming possible to enter the region of instability above the line b--b with less and less speed change as the speed increases. The present invention provides for pressures which increase with speed as much as practicable but which are kept on the stable (lower) side of the line b-b, this result being secured by having a by-pass valve which is opened in response approximately to the square of the speed to maintain a pressure and speed relation at each speed.

In the drawings, there is shown an axial-flow compressor l0 driven by a prime mover, such as the turbine H, the compressor having an inlet l2 and a delivery conduit ll provided with a bypass l5 having a by-pass valve l6. Normally, the by-pass valve I6 is closed and it is controlled jointly by speed and delivery pressure effects to maintain, at each speed, a compressor speed and delivery pressure relation such that surging is avoided.

As the pressure at which surging occurs varies approximately as the square of the compressor,

speed, the controlling speed effect is arranged to vary in the same way, such effect being developed by the control device, at l8, comprising an'abutment I9 movable against a spring by liquid under pressure furnished from the centrifugal impeller 2| driven by the compressor and supplied with liquid through 'the orifice 22.

The compressor delivery pressure controlling the operating piston, if the latter movement is in the direction to open the bleeder valve or to close it if open, until the latter changes the force of the follow-up spring to'balance the changed force of controlling liquid pressure with the relay restored to cutoff or neutral position.

In operation, to meet variable demands, the

turbine power is changed to change the speed of effect is developed by a pressure-responsive detrolling pressure in the space, at 28, and which pressure is used to control operation of the servomotor, at 30, for moving the bleeder or by-pass valve l6.

' The abutments l9 and are shown as pivotally connected at 3| and 32, respectively, to opposite ends of the floating lever 33, which is pivotally connected at an intermediate point 34 to the valve 21, the arrangement being such that increases and decreases in delivery pressure are applied through the lever to the valve to increase and decrease, respectively, the controlling pressure and increases and decreases in speed provide increasing and decreasing pressures applied through the lever to the valve to decrease and increase, respectively, the controlling pressure. With this arrangement, therefore, a change in the compressor, the compressor speed being increased for increased flow and vice versa. As the pressure at which surging takes place varies approximately as the square of the speed, the compressor is equipped with a bleeder or by-pass valve, means for opening the valve in response to delivery pressure, and means responsive to compressor speed for varying the delivery pressure required for opening the bleeder or by-pass valve. More particularly, a change in compressor speed produces a change in controlling, liquid pressure to move the by-pass valve servo-motor relay from neutral or cutofl position. If the speed increases, the controlling-liquid pressure decreasesand the relay moves for servo-motor operation to close the already-closed by-pass valve. On the other hand, if the speed decreases, the

controlling-liquid pressure increases and the relay moves for servo-motor operation to open the normally-closed by-pass valve. Therefore, an increase in speed is eii'ective to increase the comspeed is accompanied by adjustment of the valve I 21 to change the controlling liquid pressuraand speed with the delivery pressure kept under control to avoid the development of surge pressures.

The space, at 28, is furnished with oil from a suitable pressure source through an orifice andit has an escape port 36 bounded by a seat 31 with which the valve 21 cooperates to provide a variable orifice escape area; and as liquid under controlling pressure is applied to the-valve tending to open it to reduce the pressure, it will be apparent that such valve moves to keep the controlling liquid pressure force acting thereon ,in

= balance with the lever force applied thereto and derived from the pressure-responsive abutments,

'pressor delivery pressure and vice versa; and, as the controlling-liquid pressure is at all times-subject to the influence of delivery-pressure, changein the latter pursuant to speed change is effective to compensate the controlling-liquid pressure for change therein due to speed change, whereby the increase in speed, to avoid the development of surge pressures at different speeds. As the surge pressure varies approximately as the square of the speed and as the controlling arrangement is at all times subject to a controlling effect varying approximately as the square of the speed, to suit the demand, the compressor may be increased I and decreased in speed with the delivery pressure increasing and decreasing in relation thereto while being limited to avoidsurge pressures at diflerent'speeds. v

While the invention has been shown in but one form, it will be obvious to those skilled in the art in consequence of. which the opposed forces acting on the valve are kept in proportional relation.

The servo-motor, at 30, includes an operating I piston 38 mechanically connected to the bleeder valve IS, a cylinder 39 for the piston; anda relay 40 for controlling admission and "exhaust of motive fluid from the cylinder to move the piston. The relay 40 is moved by means of controlling liquid pressure-applied tothe relay piston-4| and a follow-up spring 42 engaged bya-follow-up lever 43 mechanically connected to the operating that it isnot so limited, but is susceptible of various changes and modifications without 'de- Y parting from the spirit thereof.

What is claimed is I 1. Apparatus providing for stable operation of compressor forvarying the deliverypressure re I I quired for opening the by-pass valve such that the required delivery pressure varies approxle mately as the square of the speed.

2. Apparatus providing for stable operation of a compressor at variable speeds, said apparatus including a normally-closed delivery by-pass valve, means providing controlling force, means responsive to the controlling force for operating the by- Y value is required to open the valve. means ior varying the controlling. iorce as a iunction oi compressor speed to reduce the controlling i'orce with increase in speed and vice versa, and means for var ing the controlling force directly as the delivery pressure, whereby change in controlling iorce due to speed change is compensatedby change therein due to delivery pressure change pursuantto speed change to restore the controlling force to normal value with the by-pas's valve closed.

3. In a variable speed axial-flow compressor, a normally-closed by-pass valve, a pressure-responsive servo-motor for operating the by-pass valve, means providing a space for liquid under controlling pressure, means responsive to delivery pressure for varying the controlling pressure such that an increase in delivery pressure is accompanied by an increase in controlling pressure and vice versa, means providing a pressure varying approximately as the square of the compressor speed, means for varying the controlling pressure inversely in relation to the last-named pressure, and a servo-motor for operating the by-pass valve in response to said controlling pressure.

4. Apparatus providing for stable operation of a compressor at variable speeds, said apparatus comprising a normally closed by-pass valve, means providing a space ior liquid under controlling pressure, means responsive to compressor delivery pressure for varying the controlling pressure in said space such that increase in delivery pressure is accompanied by an increase in controlling pressure and vice versa, means providing a pressure varying approximately as the square of the compressor speed, means ior varying the controlling pressure inversely in relation to the last-named pressure, and a servo-motor for operating the by-pass valve in response to controlling pressure.

6. Apparatus providing for stable operation of an axial-flow compressor at variable speeds, said apparatus comprising a compressor delivery bypass valve, means providing a space for liquid under controlling pressure, a valve operable to vary the-pressure in said space, means for operating the last-named valve in response to compressor delivery pressure and speed such that the pressure in said space isvaried directly as the delivery pressure and inversely approximately as the square of the speed, and means for operating the icy-pass valve in response to controlling liquid pressure in said space. 4

'7. Apparatus providing for stable operation of a compressor at variable speeds, said apparatus comprising a compressor delivery by-pass valve, means providing a space for liquid under controlling pressure, a valve operable to vary the pressure in said space, means for operating the lastnamed valve in response to compressor delivery pressure and speed such that the pressure in said space is varied directly as the'delivery pressure and inversely approkimately as the squared the speed. an operating piston mechanically connected to the by-pass valve, a relay for the operating piston, a follow-up connection between the operating piston and relay and including a spring, and means for applying liquid under controlling pressure to the relay to exert force thereon in opposition to that o! the follow-up spring.

8. Apparatus providing for stable operation of a compressor at variable speeds, said apparatus comprising a compressor delivery by-pass valve. means providing a space for liquid under controlling pressure, a valve operable to control the pressure of liquid in said space, a floating lever having said valve connected thereto at an intermediate point, first and second pressure-responsive devices connected to the opposite ends of the floating lever, said pressure-responsive devices being arranged so that increase in pressure applied to the first device is effective to move the valve to increase the controlling pressure and vice versa and increase in pressure applied to the second pressure-responsive device is effective to move the valve to reduce the controlling pressure and vice versa, means providing for application of delivery pressure to the first pressureresponsive device, an impeller driven by the compressor for supplying fluid under pressure to the second pressure-responsive device, an operating piston mechanically connected to the by-pass valve, a relay for the operating piston, a followup connection between the operating piston and the relay and including a spring, and means for applying liquid under controlling pressure to the relay to exert force thereon in opposition to that of the follow-up spring.

9. Apparatus providing for stable operation of a compressor at variable speeds, said apparatus comprising a normally-closed compressor delivery by-pass valve, means providing a space for liquid under controlling pressure, means responsive to liquid under controlling pressure for operating the by-pass valve, means for varying the controlling pressure of liquid in said space and 'including a pressure-controlling valve cooperating with its seat to define a variable escape orifice area for said space,- means for applying to'the pressure-controlling valve force varying approximately as the square of the speed oi the compressor to decrease the space pressure with increase in speed and vice versa, and means for applying compressor delivery pressure to the pressure-controlling valve tocompensate the space pressure for change therein pursuant to speed change to maintain the by-pass valve normally closed.

10. Apparatus providing for stable operation 0!.

a compressor at variable speeds, said apparatus comprising a normally-closed compressor delivery icy-pass valve; means providing a. space for liquid under controlling pressure; a servo-motor for operating said by-pass valve in response to liquid under controlling pressure; said servo-motor including an operating piston mechanically connected to the by-pass valve, a cylinder for the piston, a relay movable in an opposite direction from a neutral or cutofl position to admit and exhaust motive fluid to opposite ends of the cylinder to move the operating piston, 'Ioliow-up means connecting the operating piston and the relay, and means for operating the relay ncluding a spring forming a partof the follow-up connection and a piston acted on by liquid under controlling pressure so that the force thereof 01 auaaas poses the spring force; means ior varying the pressure ofliquid in said space and including a pressure-controlling valve cooperating with its seat. to define a variable escape orifice area for 7 said space; means for applying to said pressurethe compressor delivery pressure to compensate the space pressure for change therein pursuant Q to speed change'to restore said relay to neutral or cutoii position position.

with the i y-p$s valve in closed i mimosa I. 'ponomaam.

. The following references file of this patent:

REFERE ES CITED. v I

are of record in the- UNITED s'ra' rms rams Number I 1,557,427 2,404,324 

